The long range goal of this project is to understnad the biochemical basis for the exchange and maintenance of genetic information in Escherichia coli. This organism provides an excellent model system for analysis of these events because of the wealth of genetic information delineating the existence of multiple pathways for both DNA repair and genetic recombination. To help achieve our objectives, the experiments outlined in this proposal will focus on three enzymes which have been implicated in genetic recombination, DNA repair and spontaneous mutagenesis. These proteins are DNA helicase II (uvrD), exonuclease I (sbcB), and exonuclease V (recB recC recD). In addition, the role of the newly discovered recX gene in genetic recombination and cell viability will be examined. Specific questions to be addressed include: 1. The genetic and biochemical characterization of temperature sensitive uvrD mutants; 2. Analysis of exonuclease V structure and function using monoclonal antibodies and various mutants; 3. Determination of the role of exonuclease I in the control of the SOS response; and 4. Biochemical and genetic analysis of the recX gene product. Genetic and biochemical approaches will be used to examine the catalytic properties of purified mutationally altered and wild type gene products in an effort to understand their mechanistic roles in DNA repair and genetic recombination.